The invention relates to a planetary type traction roller transmission whose transmission ratio is variable between two predetermined values.
A planetary type traction roller transmission consists of a traction ring having a sun roller disposed therein and planetary rollers arranged in the annular space between, and in firm engagement with, the sun roller and the traction ring for the transmission of motion between the sun roller and the traction ring. The sun roller is so arranged that its axis is parallel to, but spaced from, the axis of the traction ring such that an annular space of varying width is formed between the sun roller and the traction ring and the traction rollers are so arranged in this annular space that at least one of them is pulled by reaction forces into a narrowing section of the annular space when a torque is transmitted thereby causing firm frictional engagement of the traction rollers with the sun roller and the traction ring.
While such transmissions are efficient, quiet running and quite inexpensive to manufacture, they provide only for one transmission ratio. The use of two such transmissions with different transmission ratios and clutches permitting engagement of a desired one of the transmission's would render such transmission substantially more expensive such that they may not be competitive with gear shift transmissions.
For certain applications, however, it would be desirable to provide a simple and inexpensive traction roller transmission with at least two different transmission ratios such that a machine equipped with such a transmission can be operated in two different speed ranges.